Field of the Invention
The present invention relates to a method of manufacturing an external cover edge of a molded cup lid and a product manufactured by the method and, more particularly to the product made of plant fibers and the manufacturing method that adopts two techniques, respectively: “pulp suction shaping” and “thermal compression shaping” to produce an intermediate product of the molded cup lid, then forms a protruding-out outer cover edge around the periphery of the intermediate product, and finally produces the molded cup lid product.
Description of the Related Art
In general, a conventional disposable cup lid is made of a plastic material, such as polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC), and is manufactured by plastic injection molding. Such cup lid is commonly known as “plastic cup lid”. As to recycling and disposal, the conventional plastic cup lid causes a serious pollution issue. Particularly, when the quantity is large, the recycling process is difficult, and the plastic cup lid leads to serious damage to the environment. The disposable cup lid made of plastic totally departs from the concept of environmental protection. Since the conventional plastic cup lid is manufactured by plastic injection molding, the moving space required for demolding is limited, so that the plastic cup lid product fails to meet the requirement of covering the mouth of the paper cup closely. After the lid is combined with the mouth of the paper cup, the lid may be loosened or separated from the mouth of the paper cup to cause a leakage of the beverage contained in the paper cup and to raise a safety concern.
At present, mixtures such as pulp and plant fiber are used as materials to make cup lids, and the cup lids are manufactured by molds through the pulp suction shaping and thermal compression shaping technologies, and such cup lid is called “molded cup lid” or “paper cup lid”, which has a significantly different terminology with respect to the plastic cup lid. Therefore, the terms “molded cup lid’ and “paper cup lid” mentioned in the present invention refer to the objects with the same properties. To meet the requirements of covering the molded cup lid product onto the mouth of the paper cup and preventing leakage of the beverage, the ideal relative covering relation between the molded cup lid 10 and the paper cup body 20 is shown in FIGS. 1 and 2. The molded cup lid 10 has a top ring portion 11, whose internal periphery may be designed with a height drop to enhance the strength of the cover portion 111. The outer side of the top ring portion 11 is descended gradually from an outer arc edge 112 and slightly expanded outward to form a peripheral portion 12, then extended outward when reaching an inner arc edge 121, further covered downwardly and inwardly to form an outer cover edge 13 with the lowest point extended inwardly to form an inverted-hook groove 14, and then outwardly deviated to form a lift wall 15. The paper cup body 20 has a covered ring 21 with an expanded external diameter formed at the mouth of the cup, and a concave annular ring groove 22 formed at a joint of the bottom of the covered ring 21 and the paper cup body 20. During use, the molded cup lid 10 is covered onto the mouth of the paper cup body 20. At first, the molded cup lid 10 cannot be covered onto the mouth of the paper cup body 20 completely. Thus, it is necessary to apply a force to cover the outer cover edge 13 at a side of the molded cup lid 10 onto the covered ring 21 at the corresponsive position of the paper cup body 20 as much as possible, and then further apply a force to slightly, rotate the remaining outer cover edge 13 outward to force it to pass the remaining covered ring 21, so that the outer cover edge 13 totally encloses the covered ring 21 tightly, so that and the inverted-hook groove 14 of the molded cup lid 10 is pressed precisely into the concave annular ring groove 22 at the bottom of the covered ring 21 to enhance the covering stability between the outer cover edge 13 and the covered ring 21.
In FIGS. 1 and 2, the molded cup lid 10 has the double structure of the outer cover edge 13 and the inverted-hook groove 14, which is an important factor for covering the molded cup lid 10 onto the paper cup body 20 tightly. In actual manufacture, the inverted-hook groove 14 of the molded cup lid 10 cannot be formed directly, and it is necessary to form an intermediate product 100 of the molded cup lid as shown in FIG. 3 first. In other words, the intermediate product 100 is a general molded product processed by the “pulp suction shaping” and “thermal compression shaping” processes. Now, the intermediate product 100 has the top ring portion 11, the cover portion 111, the outer arc edge 112, the peripheral portion 12, the inner arc edge 121 and the lift wall 15, and a partially formed outer cover edge 13, but without the existence of the inverted-hook groove 14. The reason resides on that the limitation of the moving space required for demolding the intermediate product 100 after the “thermal compression shaping” process takes place, so that the lower section of the outer cover edge 13 cannot be formed inwardly in a negative angle. Therefore, it is necessary to perform the shaping vertically in the up and down status first. As a result, the intermediate product 100 as shown in FIG. 3 is formed first, and, then, the intermediate product 100 is processed with a compression and deformation process before the lower section of the outer cover edge 13 can be shaped inwardly with a negative angle, to form the structure of the inverted-hook groove 14.
With reference to FIGS. 4 and 5 for the compression and deformation process of a conventional intermediate product 100, an outer mold 30 is covered onto the intermediate product 100. The outer mold 30 is configured to be corresponsive to a side profile of the intermediate product 100, and a transverse annular side groove 311 is formed at a position of the outer mold 30 where the inverted-hook groove 14 is formed on the intermediate product 100 for receiving a group of shaping slide blocks 32. The internal periphery of the shaping slide blocks 32 has a protruding-out shaping ridge 321, such that when the shaping ridges 321 are moved forward and inward together, all of the shaping ridges 321 can be conjoined into an annular body. An inner mold 33 is received into the intermediate product 100. A material-propping block 34 is contained in the middle of the inner mold 33, and the material-propping block 34 has a profile corresponsive to the intermediate product 100. However, the inner mold 33 has a recessed receiving groove 331 formed at a position of the intermediate product 100 where the inverted-hook groove 14 is formed, and the location and profile of the recessed receiving groove 331 correspondingly match with those of the shaping ridge 321. When the molds of the outer mold 30 and the inner mold 33 together with the material-propping block 34 are closed as shown in FIG. 4 and the shaping slide blocks 32 are pushed to move inward, the shaping ridges 321 abut the outer surface of the intermediate product 100, and move forward continuously to let the shaping ridge 321 resist the surface of the intermediate product 100 and be deformed and contracted into the receiving groove 331 of the inner mold 33. Therefore, an annular inverted-hook groove 14 is formed on the intermediate product 100 as shown in FIG. 5, and the lower section of the outer cover edge 13 produces a negative angle inwardly, to form a product of the molded cup lid 10. Then, the shaping slide blocks 32 are withdrawn outward, and the outer mold 30 and the inner mold 33 are opened in a direction opposite to the closing direction. The material-propping block 34 props the molded cup lid 10 out to complete the whole process.
Although the manufacturing process as shown in FIGS. 4 and 5 completes the manufacture of the molded cup lid 10, the molded cup lid 10 so manufactured still has the following drawbacks. Since the intermediate product 100 is formed by using the “pulp suction shaping” and “thermal compression shaping” processes, the shape and profile are fixed. The inverted-hook groove 14 formed on the stably shaped intermediate product 100 is manufactured by compression, and the inverted-hook groove 14 is situated at an unstably formed position of the molded cup lid 10, so that a slight natural withdrawal (in the direction opposite to the compression) is formed at the inverted-hook groove 14 and the lower portion of the outer cover edge 13 due to the effect of the plastic material while the cup sits still as shown in FIG. 6. Since the withdrawal is very small, the appearance does not show, but when the molded cup lid 10 is used to cover onto the mouth of the paper cup body 20, the following effects of forces will be confronted:
1. It is necessary to apply a force for the operation, so that the molded cup lid 10 is rotated and expanded slightly outward, and so that the compulsory restoration goes beyond the covered ring 21 of the paper cup body 20. Since the direction of applying the force is opposite to the deformation direction of the inverted-hook groove 14, therefore the inverted-hook groove 14 will be withdrawn in a direction opposite to the direction of compression.
2. Since the paper cup body 20 is generally used for containing a hot beverage, heat is transmitted upwardly and outwardly, so that the inverted-hook groove 14 will also be withdrawn in a direction opposite to the direction of compression.
3. The inverted-hook groove 14 and the lower section of the outer cover edge 13 of the molded cup lid 10 are withdrawn naturally. Thus, the beverage contained in the paper cup body 20 may leak easily after the molded cup lid 10 is covered onto the mouth of the paper cup due to the joint effect of the withdrawals by force and heat, or the molded cup lid 10 may be loosened or separated from the paper cup body 20. Such conventional design fails to meet the requirement of covering the molded cup lid 10 onto the paper cup body 20 tightly or to prevent hot beverage from leaking out from the paper cup.